MIMO transmitter and methods for transmitting OFDM symbols with cyclic-delay diversity

ABSTRACT

A multiple-input multiple output (MIMO) transmitter and methods for transmitting orthogonal frequency division multiplexed (OFDM) symbols with cyclic-delay diversity (CDD) are generally described herein. In some embodiments, a base station uses a number of antennas for MIMO transmission of OFDM symbols. For the number of antennas, quadrature-amplitude modulated (QAM) symbols are distributed across a group of OFDM tones of a block comprising the group of tones and a group of OFDM symbols. An incremented cyclic delay is applied to the QAM symbols of the block associated with each subsequent of the antennas for CDD transmission. Each blocks is transmitted by an associated one of the antennas.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/750,549, entitled “METHODS AND APPARATUS TO CONTROL TRANSMISSION OF AMULTICARRIER WIRELESS COMMUNICATION CHANNEL THROUGH MULTIPLE ANTENNAS,”filed on Dec. 31, 2003, now issued as U.S. Pat. No. 7,769,097, whichclaims priority under 35 U.S.C. 119(e) to U.S. Provisional PatentApplication Ser. No. 60/503,092, filed on Sep. 15, 2003, by Shao, etal., entitled “An Apparatus and Associated Methods to Implement aHigh-Throughput Wireless Communication System,” all of which areexpressly incorporated herein by reference in their entireties.

TECHNICAL FIELD

Embodiments of the present invention are generally directed to awireless communication system and, more particularly, to methods andapparatus to control transmission of a multicarrier wirelesscommunication channel through multiple antenna(e).

BACKGROUND

A multicarrier communication system such as, e.g., Orthogonal FrequencyDivision Multiplexing (OFDM), Discrete Multi-tone (DMT) and the like, istypically characterized by a frequency band associated with acommunication channel being divided into a number of smaller sub-bands(subcarriers herein). Communication of information (e.g., data, audio,video, etc.) between stations in a multicarrier communication system isperformed by dividing the informational content into multiple pieces(e.g., symbols), and then transmitting the pieces in parallel via anumber of the separate subcarriers. When the symbol period transmittedthrough a subcarrier is longer than a maximum multipath delay in thechannel, the effect of intersymbol interference may be significantlyreduced.

While multicarrier communication systems hold the promise of highthroughput communication channels, technical challenges persist. Forexample, in certain applications such as, for example a wireless localarea network (WLAN) deep fades can occur in the channel that may persistover a significant period of time. Further, due to environmentalconditions (e.g., home office, business, etc.), the wireless channelsmay typically encounter significant dispersion due to multipathpropagation that limits the maximum achievable rates.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention are illustrated by way of example,and not by way of limitation, in the figures of the accompanyingdrawings in which like reference numerals refer to similar elements andin which:

FIG. 1 is a block diagram of an example multicarrier wireless networkincorporating the teachings of the present invention, according to oneexample implementation;

FIG. 2 is a block diagram of an example transceiver incorporating theteachings of the present invention, according to one exampleimplementation;

FIG. 3 is a flow chart of an example method for mapping information toone or more antenna(e) and subcarrier(s), according to one embodiment ofthe invention;

FIG. 4 is a flow chart of an example method for mapping information toone or more antenna(e) and subcarrier(s), according to one embodiment ofthe invention;

FIGS. 5 and 6 provide graphical illustrations of transmit diversity andspace-frequency interleaving for two transmit antennas, in accordancewith embodiments of the present invention;

FIG. 7 is a graphical illustration of the improvement to one or morechannel characteristics through use of an embodiment of the invention;

FIG. 8 provides a graphical illustration of the improvement to one ormore channel characteristics through use of an embodiment of theinvention; and

FIG. 9 is a block diagram of an example article of manufacture includingcontent which, when executed by an accessing machine, causes the machineto implement one or more aspects of embodiment(s) of the invention.

DETAILED DESCRIPTION

Embodiments of an apparatus and associated methods to controltransmission of a multicarrier wireless communication channel aregenerally introduced herein. In this regard, aspects of the presentinvention may well be used to implement any of a number of wirelesscommunication platforms such as, e.g., wireless local area network(WLAN), wireless personal area network (WPAN), wireless metro-areanetworks (WMAN), cellular networks, and the like.

With this disclosure, an innovative approach to improving the resilienceof the multicarrier communication channel is disclosed, wherein anadvanced OFDM processing technique is added to a multiple input,multiple output (MIMO) transceiver that utilizes more than onetransmit/receive chain at each end of the wireless link. Those skilledin the art will appreciate, in view of the following discussion, thatthe disclosed combination of MIMO and OFDM (MIMO-OFDM) appearsparticularly promising for high-throughput wireless LAN application.

According to a first aspect of the invention, a transmit diversitycapability is introduced, which provides a near-optimal method formapping uncoded content (e.g., quadrature amplitude modulation (QAM)symbols) received from a host device, or an application/agent executingthereon, to multiple antennas and OFDM tones. While the transmitdiversity architecture introduced herein provides full-order diversity,it may only provide a limited code rate per OFDM slot.

According to another aspect of the invention, the transmit diversityarchitecture is extended to provide a higher code rate by means ofspace-frequency interleaving (SFI). As developed more fully below, SFIprovides a near-optimal technique for mapping coded information (e.g.,bits, frames, symbols, etc.) onto multiple antennas and OFDM tones.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present invention. Thus, appearances of the phrases“in one embodiment” or “in an embodiment” in various places throughoutthis specification are not necessarily all referring to the sameembodiment. Furthermore, the particular features, structures orcharacteristics may be combined in any suitable manner in one or moreembodiments.

Example Network Environment

FIG. 1 illustrates a block diagram of a wireless communicationenvironment within which the teachings of the present invention may bepracticed. As shown, network 100 depicts two devices 102, 104, eachcomprising one or more wireless transmitter(s) and receiver(s)(cumulatively, a transceiver) 108, 116, baseband and media accesscontrol (MAC) processing capability 112, 114, and memory 110, 118, eachcoupled as shown. As used herein, the devices 102, 104 communicateinformation between one another via a multicarrier wirelesscommunication channel 106, established between the transceiver(s) 108,116 through one or more antenna(e) associated with the devices.According to one embodiment, one of the devices 102 may be coupled toanother network 120.

According to one aspect of the invention, an innovative diversity agentis introduced within the device(s) introduce and manage one or moreelements of diversity within the multicarrier wireless channel. On thetransmit side of a communication channel, the diversity agent mayselectively map content (e.g., received from a host device, application,agent, etc.) to one or more antenna(e) and/or OFDM tones to generate aMIMO-OFDM transmit signal. In support of the receive side of thecommunication channel, the diversity agent may selectively demap thecontent received via the MIMO-OFDM wireless channel (e.g., 106) frommultiple antennas and OFDM tones. While not specifically denoted in FIG.1, the diversity agent may well be implemented in one or more of thebaseband and MAC processing element(s) (112, 114) and/or the transceiverelement(s) (108, 116), although the invention is not so limited.

According to one example embodiment, the diversity agent may selectivelyprocess content received from the host device (e.g., 102, 104) toimplement full-order transmit diversity, although the invention is notlimited in this respect. As developed below, diversity agent may mapuncoded content (e.g., quadrature amplitude modulated (QAM) symbols)received from the host device (102, 106) or applications executingthereon, onto multiple antennas and OFDM tones to effect spatialdiversity in the transmit link of channel (106).

According to one embodiment, the diversity agent may selectively processcontent received from the host device (e.g., 102, 104) to introducespace-frequency interleaving (SFI) of the content onto multiple antennasand OFDM tones. In this regard, as developed below, diversity agent mayselectively map coded information (e.g., bits, bytes, blocks, symbols,frames, packets, etc.) received from the host device or applicationsexecuting thereon, onto multiple antennas and OFDM tones by performingone or more of antenna multiplexing, 802.11a interleaving, QAM mapping,and cyclic tone shifting, although the invention is not limited in thisregard.

In addition to the foregoing, the diversity agent may selectivelyimplement an innovative technique(s) for decoding information from areceived OFDM channel processed as above. In this regard, an innovativereceive diversity agent is introduced to demap and/or deinterleavecontent received from a channel 106 generated in accordance with one orboth of the encoding techniques introduced above. According to oneembodiment, receive diversity agent receives content as decodedmodulation information (e.g., bits) and generates de-mapped and/orde-interleaved content, respectively.

But for the introduction of the diversity agent introduced above,devices 102, 104 are intended to represent any of a wide range ofelectronic devices with wireless communication capability including, forexample, a laptop, palmtop or desktop computer, a cellular telephone(e.g., a 2G, 2.5G, 3G or 4G handset), a personal digital assistant, anWLAN access point (AP), a WLAN station (STA), and the like.

As used herein, baseband and MAC processing element(s) 112, 114 may beimplemented in one or more processors (e.g., a baseband processor and anapplication processor), although the invention is not limited in thisregard. As shown, the processor element(s) 112, 114 may couple to memory110, 118, respectively, which may include volatile memory such as DRAM,non-volatile memory such as Flash memory, or alternatively may includeother types of storage such as a hard disk drive, although the cope ofthe invention is not limited in this respect. Some portion or all ofmemory 110, 118 may well be disposed within the same package as theprocessor element(s) 112, 114, or may be disposed on an integratedcircuit or some other medium external to element(s) 112, 114. Accordingto one embodiment, baseband and MAC processing element(s) 112, 114 mayimplement at least a subset of the features of diversity agent describedbelow, and/or may provide control over a diversity agent implementedwithin an associated transceiver (108, 116), although the invention isnot limited in this regard.

Similarly, but for the introduction of the diversity agent to effect theMIMO-OFDM channelization developed more fully below, transceivers 108,116 are also intended to reflect any of a variety of multicarrierwireless communication transceivers known in the art. In this regard, atransmitter element of the transceivers receive content from a hostdevice, process the received content to generate an OFDM transmitsignal, and then transmits that OFDM signal over a link (e.g., forwardlink) to a remote device via one or more antennae. A receiver element ofthe receivers receives multiple instances of the forward link via one ormore antenna(e), and selectively processes the received signal(s) toextract a representation of the originally encoded content. Again, theintroduction of the diversity agent enables the wireless transceiverwithin the device(s) to implement the MIMO-OFDM features describedbelow. According to one embodiment, each of the transmitters andreceivers may well include one or more processing chains.

As used herein, network 120 is intended to represent any of a broadrange of communication networks including, for example a plain-oldtelephone system (POTS) communication network, a local area network(LAN), metropolitan area network (MAN), wide-area network (WAN), globalarea network (Internet), cellular network, and the like. According toone example implementation, device 102 represents an access point (AP),while device 104 represents a station (STA), each of which suitable foruse within an IEEE 802.11n wireless local area network (WLAN), and eachutilizing the innovative space-frequency interleaving and transmitdiversity techniques introduced above, and developed more fully below.

Example Transceiver Architecture

FIG. 2 illustrates a block diagram of an example transmitterarchitecture and an example receiver architecture according to oneexample embodiment of the invention. To illustrate these architectureswithin the context of a communication channel between two devices, atransmitter from one device (e.g., 102) and a receiver from anotherdevice (e.g., 104) associated with a communication link are depicted.Those skilled in the art will appreciate that a transceiver in eitherdevice (102, 104) may well comprise a transmitter architecture and areceiver architecture as detailed in FIG. 2, although the scope of theinvention is not limited in this regard. It should be appreciated thattransmitter and receiver architectures of greater or lesser complexitythat nonetheless implement the innovative transmit diversity and/orspace-frequency interleaving described herein are anticipated by thescope and spirit of the claimed invention.

According to one example embodiment, a transmitter architecture 200 isdepicted comprising one or more of a serial to parallel transform 210, a(transmit) diversity agent 212, one or more inverse discrete Fouriertransform (IDFT) element(s) 214, a cyclic prefix, or guard interval,insertion element 216 coupled with one or more antenna(e) 220A . . . Mthrough an associated one or more radio frequency (RF) elements 218,although the invention is not limited in this regard. According to oneembodiment, transmitter architecture 200 may be implemented withintransceiver 108 and/or 116. Although depicted as a number of separatefunctional elements, those skilled in the art will appreciate that oneor more elements of transmitter architecture 200 may well be combinedinto a multi-functional element, and conversely functional elements maybe split into multiple functional elements without deviating from theinvention.

As used herein, serial-to-parallel (S/P) transform 210 receivesinformation (e.g., bits, bytes, frames, symbols, etc.) from a hostdevice (or, an application executing thereon, e.g., email, audio, video,etc.) for processing and subsequent transmission via the communicationchannel. According to one embodiment, the received information is in theform of quadrature amplitude modulated (QAM) symbols (i.e., wherein eachsymbol represents two bits, b_(i) and b_(j)). According to oneembodiment, serial-to-parallel transform 210 takes the information andgenerates a number of parallel substreams of the information, which arepassed to one or instances of diversity agent 212. Although depicted asa separate functional element, serial to parallel transform 210 may wellbe included within the diversity agent 212, or other element of thetransmitter 200.

According to one embodiment, diversity agent 212 selectively introducesan element of transmit diversity into the information streams receivedfrom the S/P transform 210. In particular, according to one exampleembodiment, the informational content is selectively mapped to one ormore antenna(e) and OFDM tones. According to one example implementation,if content received from the host device at diversity agent 212 is notin the form of QAM symbols, diversity agent may perform pre-coding tomap the received information to QAM symbols, although the invention isnot limited in this regard. Indeed, diversity agent may well introducetransmit diversity to any linear combination of input symbols.

In any case, diversity agent 212 takes the input (e.g., QAM symbols) andrepetitively disperses them (bits, symbols, etc.) across Mt transmitantennas, and a number (N) of OFDM tones for each of a plurality ofRayleigh fading channel taps (L), although the invention is not limitedin this regard. By selectively dispersing the content in this manner,full order diversity (Mt Mr L, where Mr is the number of receiveantennae) may be achieved. An example method for introducing transmitdiversity is presented below with reference to FIG. 3, and a graphicalillustration of symbols processed in accordance with an example transmitdiversity mechanism is provided in FIG. 5.

In accordance with another aspect of the invention, diversity agent 212may well include the resources to implement a space-frequencyinterleaving (SFI) mechanism. In this regard, diversity agent 212 maywell include one or more of an antenna multiplexing element, a toneinterleaving element, a QAM interleaving element, a QAM mapping elementand a cyclic tone shifting element, although the invention is notlimited in this regard. According to one embodiment, diversity agent 212may treat adjacent coded bits as one symbol, and spreads thisinformation across space and frequency, e.g., using the transmitdiversity repetition scheme introduced above. According to oneembodiment, the content received from S/P transform 210 is firstinterleaved across at least a subset of transmit antenna(e) Mt, and thenacross a number of OFDM tones for each of a plurality of the Rayleighfading channel taps (L), although the invention is not limited in thisregard. Indeed, these functional elements need not necessarily beapplied in the order described above. Moreover, the amount of cyclictone shift may well be modified to any value between zero (0) and thenumber data tones (Nds), and there may be a cyclic shift across antennasinstead of, or in addition to the shift across tones. An example methodfor implementing the space-frequency interleaving is developed morefully below, with reference to FIG. 4, and a graphical representation ofSFI is presented with reference to FIG. 6.

In either case, content from the transmit diversity agent 212 is passedto one or more inverse discrete Fourier transform (IDFT) element(s) 214.According to one embodiment, an inverse fast Fourier transform (IFFT)element(s), although the invention is not limited in this regard.According to one embodiment, the number of IDFT elements 214 iscommensurate with the number of transmit antenna(e), i.e., transmitradio frequency (RF) chains. In this regard, IDFT element(s) 214 mayreceive a plurality (Z) of encoded substreams from the diversity agent212, and converts the content from a frequency domain representation toa time domain representation of the content, although the invention isnot limited in this regard.

The time domain content from the IDFT element(s) 214 is passed to CPIelement(s) 216. According to one embodiment, CPI 216 may introduce acyclical prefix, or a guard interval in the signal, before it is passedto a radio frequency (RF) front-end 218 for amplification, filtering andsubsequent transmission via an associated one or more antenna(e) 220A .. . M.

To extract content processed by a transmitter architecture 200, above,an example receiver architecture 250 is introduced. As shown, an RFfront-end 254 receives a plurality of signals impinging on one or morereceive antennae 240A . . . N. For ease of explanation and descriptiongoing forward, in accordance with one example embodiment, the number (N)of receive antenna(e) is equal to Mr. According to one embodiment, eachreceive antenna has a dedicated receive chain, where the number ofreceive front-end elements 254, CPR elements 256 and FFT elements arecommensurate with the number (N) of receive antenna(e) (e.g., Mr).

The RF front end 254 may pass at least a subset of the receivedsignal(s) to a cyclic prefix removal element(s) 256, although theinvention is not limited in this regard. According to one embodiment,CPR 256 removes any cyclic prefix or guard interval that may have beenintroduced during transmit processing of the received signal(s).

The content from CPR 256 is then provided to an associated one or moreof fast Fourier transform (FFT) element(s) 258. According to oneembodiment, FFT elements 258 transform the received signals from anassociated receive chain from the time domain to the frequency domain,for subsequent demultiplexing and decoding of a representation of thecontent embedded within the received transmission. Thus, a plurality offrequency domain representations of the received signal(s) are presentedto receive diversity agent 260.

According to one aspect of the present invention, receive diversityagent 260 may perform a complementary function to that performed bytransmit diversity agent 212. In this regard, receive diversity agent260 may perform the complement to the transmit diversity and/or spacefrequency interleaving introduced above. In the case of transmitdiversity, receive diversity agent 260 may demap the QAM symbols, priorto QAM demodulation and parallel to serial conversion 262 to extract arepresentation (I′) of the content encoded within the receivedsignal(s). In the case of SFI, receive diversity agent 260 performsdeinterleaving and decoding, before providing the output content to theparallel to serial converter 262 which generates the representation (I′)of the content encoded within the received signal(s). According to oneembodiment, diversity agent 260 may well implement a minimum mean squareerror (MMSE) spatial demapper followed by soft Viterbi decoding,although the invention is not limited in this regard.

Although depicted as a number of functional blocks, those skilled in theart will appreciate that one or more of the foregoing elements may wellbe implemented in hardware, software, firmware, or any combinationthereof. Moreover, although not explicitly denoted, it will beappreciated by those skilled in the art that one or more elements suchas, e.g., diversity agent 212, 260 may well receive control input frombaseband and/or MAC processing elements (e.g., 112, 114). According toone embodiment, diversity agents 212, 260 may well implement one or moreof transmit diversity and space-frequency interleaving, and communicatewhich MIMO-OFDM scheme is being used through an exchange of channelstate information. In this regard, diversity agent 212, 260 and thetransmit diversity/SFI techniques associated therewith, may be adaptedaccording to observed channel delay spread and transmit or receiveantenna correlation information (i.e., channel state information).

Example Diversity Agent Operation

Having briefly introduced an example network environment and diversityagent architecture, above, a discussion of each of the MIMO-OFDMtechniques introduced herein will now be developed more fully withreference to FIGS. 3-7. For ease of description and understanding, thedevelopment of these techniques will be presented in flow-chart formwith continued reference, where appropriate, to example elements inFIGS. 1 and 2, although the invention is not limited in this regard.

Turning to FIG. 3, a flow chart of an example method 300 forimplementing transmit diversity is disclosed, according to one exampleembodiment. As shown, the method begins with block 302, wherein thediversity agent 212 receives content for processing. According to oneexample embodiment, the received content is a plurality of substreams ofinformation received from a serial to parallel transform, although theinvention is not limited in this regard. According to one embodiment,the received content is in the form of complex symbols that are linearor nonlinear combinations of input QAM symbols. According to oneembodiment, diversity agent 212 may receive the content from a QAMmodulator, wherein the received content is in the form of QAM symbols,although the invention is not limited in this regard. According toanother embodiment, diversity agent 212 receives uncoded informationstream(s) of bits, and converts the content into QAM symbols.

In block 304, diversity agent 212 cyclically distributes the QAM symbolsacross one or more antennae and one or more OFDM tones. According to oneembodiment, diversity agent 212 captures spatial diversity through thedevelopment of Mt×N/L blocks of QAM symbols (where N is the number ofOFDM tones, and L is the number of Rayleigh fading channel taps), wherethe symbols applied to each antenna are offset by a cyclical shift. Byrepeating these frequency blocks L times across the number of OFDMtones, diversity agent 212 introduces an element of frequency diversityinto the channel as well.

According to one example embodiment, the number of frequency blocks maybe adaptively modified according to multipath conditions in the channel.In this regard, a larger delay spread among frequency blocks may beemployed by diversity agent 212 when there is high delay spread (L), andfewer blocks may be used for lower delay spread. Moreover, when there isa risk of horizontal wraparound of symbols, wherein the same symbol istransmitted on the same tone, or a very close tone, on a differentantenna, diversity agent 212 may well increase or decrease thedispersion to remove this wraparound condition, as appropriate. Agraphical illustration of the transmit diversity blocks are presentedwith reference to FIG. 5.

In block 306, the blocks generated by diversity agent 212 are providedto the remainder of the transmit processing chain (e.g., IFFT 214, etseq.) to enable the transmitter to complete channel processing on thedistributed content for transmission via the one or more antenna(e) andOFDM tones.

Turning to FIG. 4, a flow chart of an example method 400 forimplementing space-frequency interleaving (SFI) is introduced, accordingto one embodiment of the invention. As shown, the technique begins inblock 402, where diversity agent 212 receives encoded content. As above,the encoded content may be received, e.g., from forward error correcting(FEC) encoder, a convolutional encoder, a Reed Solomon encoder, and LDPCencoder, a trellis encoder, a turbo coder a BCH coder, etc., which maybe an element of diversity agent 212, although the invention is notlimited in this regard. According to one implementation, diversity agent212 may assume a sliding window memory such as that provided by aconvolutional encoder, although the invention is not limited in thisrespect. Indeed, for other codes, diversity agent 212 mayrearrange/interleave the input so as to be correlated in a slidingwindow fashion. In general, the output codeword from any code may betreated as a QAM symbol x₁, per the transmit diversity aspect describedabove, and constituent codeword bits may then be spread using thespace-frequency interleaving techniques described herein.

Diversity agent 212 may then perform antenna multiplexing on thereceived encoded information. According to one embodiment, adjacent bitsof the received content are first mapped to the Mt antennas. Forexample, assume the total number of bits=Mt*N_(CBPS), where N_(CBPS) isthe number of coded and punctured bits mapped to forty-eight (48) tonesof an OFDM symbol (as used, e.g., in accordance with the IEEE Std.802.11a (1999) specification, the disclosure of which is expresslyincorporated herein by reference for all purposes), although theinvention is not limited in this regard. The bits indexed bym:Mt:Mt*N_(CBPS) are mapped to the m^(th) antenna.

In block 404, diversity agent 212 may interleave the resulting groups ofN_(CBPS) bits on each antenna. According to one embodiment, diversityagent 212 may implement this interleaving in accordance with the 802.11ainterleaver, which consists of two elements: tone interleaving, and QAMinterleaving (see, e.g., IEEE Std. 802.11a-1999, Part 11: Wireless LANMedium Access Control (MAC) and Physical Layer (PHY) specifications,incorporated herein for all purposes).

According to one example embodiment, diversity agent 212 may ensure thatadjacent coded bits are mapped onto nonadjacent subcarriers to performthe tone interleaving. According to one embodiment, the interleaverdepth determines how many tones separate adjacent coded bits. Ingeneral, this separation should be equal to the coherence bandwidth ofthe channel, e.g., N/L_(R) (where N=DFT size, and L_(R)=the length ofthe channel response in time), although the invention is not limited inthis respect. In this regard, the interleaver depth is proportional tothe length of the channel impulse in time (L_(R)).

As used herein, according to one embodiment, interleaver depth may bedefined as the separation between bits on adjacent tones in eachfrequency block. For example, if there are 1:48 input bits to be mappedto 48 tones with a depth of 16 (i.e., per 802.11a interleaver), wherethe bits are mapped to tones 1:48 column-by-column, bits 1, 17, 33 and 2are mapped to tones 1, 2, 3 and 4, respectively. More particularly, themapping would look like:

$\begin{matrix}1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 & 11 & 12 & 13 & 14 & 15 & 16 \\17 & 18 & 19 & 20 & 21 & 22 & 23 & 24 & 25 & 26 & 27 & 28 & 29 & 30 & 31 & 32 \\33 & 34 & 35 & 36 & 37 & 38 & 39 & 40 & 41 & 42 & 43 & 44 & 45 & 46 & 47 & 48\end{matrix}$

If we change the depth to 12, we get the following mapping, where bits1, 13, 25, 37 and 2 are mapped to tones 1, 2, 3, 4 and 5 respectively:

$\begin{matrix}1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 & 11 & 12 \\13 & 14 & 15 & 16 & 17 & 18 & 19 & 20 & 21 & 22 & 23 & 24 \\25 & 26 & 27 & 28 & 29 & 30 & 31 & 32 & 33 & 34 & 35 & 36 \\37 & 38 & 39 & 40 & 41 & 42 & 43 & 44 & 45 & 46 & 47 & 48\end{matrix}$

According to one example embodiment, diversity agent 212 may adapt theinterleaver depth to the observed value of L. Depending on perceivedmultipath conditions, a high L will result in a large interleaver depth,and vice versa. According to one embodiment, diversity agent 212 may setthe interleaver depth based on a worst case channel response condition,e.g., where L=worst case delay spread=length of the cyclic prefix of anOFDM symbol (e.g., 16 in an 802.11a compliant system).

Thus, for arbitrary values of N (e.g., 96 or 108 when multiple 802.11achannels are bonded together to provide high throughput), a key designcriterion that determines performance contemplated by the diversityagent 212 is the separation of adjacent coded bits as a function of thechannel's coherence bandwidth. If the channel bandwidth increases as inchannel bonding without affecting inter-tone spacing, the coherencebandwidth will not change (over the same set of multipath channels). Ifa larger DFT size is taken within the same channel bandwidth, diversityagent 212 may change the tone spacing such that adjacent coded bits areseparated accordingly by a proportionally larger number of tones.

To perform QAM interleaving, diversity agent 212 may ensure thatadjacent coded bits are mapped alternately onto less and moresignificant bits of the constellation and, as such, long runs of lowreliability (LSB) bits are avoided. According to one example embodiment,diversity agent 212 performs the tone and QAM interleaving in accordancewith the following mathematical descriptions, respectively:i=(N _(CBPS)/16)(k mod 16)+floor(k/16)  [1]where k=0, 1, . . . , N_(CBPS-1); and the function floor denotes thelargest integer not exceeding the parameter.j=s×floor(i/s)+(i+N _(CBPS)−floor(16×i/N _(CBPS)))mod s  [2]where the value of s is determined by the number of coded bits persubcarrier, N_(BPSC), according to s=max(N_(BPSC)/2,1). According to oneembodiment, a diversity agent 260 in a receiver may employ adeinterleaver which performs the inverse relation defined by the abovetwo permutations, although the invention is not limited in this regard.

In block 406, diversity agent 212 may map the interleaved content to QAMsymbols. According to one embodiment, diversity agent 212 may include abit-to-QAM mapper, wherein multiple bits are mapped to the QAM symbols.According to one example embodiment, the OFDM subcarriers are modulatedusing BPSK, QPSK, 16-QAM, 64-QAM, 128-QAM or 256-QAM, depending on thecoding rate to be employed, but the scope of the invention is notlimited in this regard. According to one embodiment, the encoded andinterleaved binary serial input data may be divided into groups ofN_(BPSC) (e.g., 1, 2, 4 or 6) bits and converted into complex numbersrepresenting QAM constellation points. The conversion may be performedaccording to Gray coded constellation mappings, although the inventionis not limited in this respect.

In block 408, diversity agent 212 introduces a cyclic shift to theresultant QAM symbols on each antenna with respect to the otherantenna(e). According to one embodiment, as introduced above, diversityagent 212 shifts the symbols destined for the m^(th) antenna by m−1tones vis-à-vis the 1^(st) antenna. As used herein, the cyclic toneshift introduced by diversity agent may well be greater than 1. Indeed,according to one embodiment, the cyclic tone shift introduced bydiversity agent 212 is adaptive based, at least in part, spatialcorrelation—the more correlated the fading on different antennas, thegreater the tone shift from antenna to antenna. In certainimplementations, e.g., where the number of transmit antennas (Mt) ishigh, diversity agent may shift by more than one tone from antenna toantenna to avoid wrap around and ensure good performance.

In this regard, according to one embodiment, diversity agent 212 mayrepeat each bit Mt times, and then perform the SFI technique introducedherein on the larger coded sequence. For example, if the original codedbit sequence is [b1, b2, b3, b4] and there are two transmit antennas(Mt=2), diversity agent 212 may expand the received bit sequence to [b1b1 b2 b2 b3 b3 b4 b4]. It should be appreciated, from the disclosureherein, that there may be other ways to expand each the coded sequencerather than simple repetition, e.g., by taking into account theresulting multidimensional space-frequency constellations, etc.

The space-frequency interleaved blocks are then processed fortransmission via one or more antenna(e) and OFDM tones, as introducedabove. An example graphical illustration of the space-frequencyinterleaved blocks generated by diversity agent 212 is provided withreference to FIG. 6, below.

Although not particular detailed, those skilled in the art willappreciate from the discussion above, that a receive diversity agent 260may implement selectively implement either of the foregoing methods in acomplementary (e.g., reverse) order to demap, or deinterleave,respectively, content received on signals processed in accordance withthe above transmit diversity or space-frequency interleaving techniques.For example, the deinterleaving technique may comprise one or more ofcyclically shifting the tones, QAM to bit mapping, deinterleaving, andantenna demultiplexing, although the invention is not limited in thisregard.

Turning to FIG. 5, a graphical illustration of an example transmitdiversity blocks generated in accordance with an embodiment of theinvention is presented. In accordance with the example embodiment ofFIG. 5, a diversity block of Mt×N/L is used. In this case, diversityagent 212 generates an L number 2×N/L matrices of QAM symbols. Thetechnique illustrated in FIG. 5 is extensible to cover situations ofMt>2 by, e.g., incrementing the cyclic delay on each additional transmitantenna according to (Mt−1) on successive antennae. It should beappreciated that the space frequency codeword in FIG. 5 is from aViterbi decoder that decodes across tones while taking into account therepetition of symbols across L blocks, although the invention is notlimited in this regard.

Turning to FIG. 6 a graphical illustration of an example space-frequencyinterleaving blocks generated in accordance with an embodiment of theinvention is illustrated. As above, for ease of illustration and notlimitation, the SFI blocks depicted correspond to an embodiment whereinMt=2, but is extensible to implementations of Mt>2 in accordance withthe techniques described above.

FIG. 7 presents a graphical illustration evidencing the performancecharacteristics associated with various mapping techniques (i.e., singleinput, single output (1×1 SISO), spatial multiplexing (where bits areinterleaved across tones, but not antennae), and space-frequencyinterleaving (SFI)). According to the illustrated embodiment, FIG. 7graphically illustrates the performance (e.g., measured in bit errorrate (BER) and packet error rate (PER) over Es/No) for a 54Mbps/antenna. As shown, the SFI technique exhibits a modest gain ofabout one decibel (1 dB) in signal to noise ratio (SNR) performancerelative to conventional (simpler) techniques for a receiver consistingof an MMSE spatial demapper and a soft Viterbi decoder, but should belarger for more sophisticated receivers.

Although depicted or described as comprising a number of functionalelements, those skilled in the art will appreciate, based on thediscussion herein, that alternate embodiments of the diversity agent 212are anticipated within the scope and spirit of the invention. Accordingto one example embodiment, a diversity agent that omits the antennamultiplexing and cyclic tone shift features is anticipated. Inaccordance with this example embodiment, diversity agent may map blocksof contiguous bits to each of at least a subset of antenna(e), and thenperform 802.11a tone and QAM interleaving, and bit-to-QAM mappingdescribed above, although the invention is not limited in this regard. Adiversity agent that performs the inverse operations is alsoanticipated.

FIG. 8 depicts a graphical illustration of a performance comparison ofSFI vs. spatial multiplexing for a lower data rate of 6 Mbps pertransmit antenna. As shown, the performance improvement introduced bySFI is more pronounced at lower data rates. Thus, it should beappreciated from the discussion herein that certain advantages of theproposed technique may be even more pronounced in realistic channelswith impairments such as antenna gain imbalance, I/Q mismatch etc.

Alternate Embodiment(s)

FIG. 9 illustrates a block diagram of an example storage mediumcomprising content which, when invoked, may cause an accessing machineto implement one or more aspects of the diversity agent 212, 260 and/orassociated methods 300, 400. In this regard, storage medium 900 includescontent 902 (e.g., instructions, data, or any combination thereof)which, when executed, causes an accessing appliance to implement one ormore aspects of SMA 212, 260, described above.

The machine-readable (storage) medium 900 may include, but is notlimited to, floppy diskettes, optical disks, CD-ROMs, andmagneto-optical disks, ROMs, RAMs, EPROMs, EEPROMs, magnet or opticalcards, flash memory, or other type of media/machine-readable mediumsuitable for storing electronic instructions.

In the description above, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It will be apparent, however, toone skilled in the art that the present invention may be practicedwithout some of these specific details. In other instances, well-knownstructures and devices are shown in block diagram form.

Embodiments of the present invention may be used in a variety ofapplications. Although the present invention is not limited in thisrespect, the circuits disclosed herein may be used in microcontrollers,general-purpose microprocessors, Digital Signal Processors (DSPs),Reduced Instruction-Set Computing (RISC), Complex Instruction-SetComputing (CISC), among other electronic components. However, it shouldbe understood that the scope of the present invention is not limited tothese examples.

Embodiments of the present invention may also be included in integratedcircuit blocks referred to as core memory, cache memory, or other typesof memory that store electronic instructions to be executed by themicroprocessor or store data that may be used in arithmetic operations.In general, an embodiment using multistage domino logic in accordancewith the claimed subject matter may provide a benefit tomicroprocessors, and in particular, may be incorporated into an addressdecoder for a memory device. Note that the embodiments may be integratedinto radio systems or hand-held portable devices, especially whendevices depend on reduced power consumption. Thus, laptop computers,cellular radiotelephone communication systems, two-way radiocommunication systems, one-way pagers, two-way pagers, personalcommunication systems (PCS), personal digital assistants (PDA's),cameras and other products are intended to be included within the scopeof the present invention.

The present invention includes various operations. The operations of thepresent invention may be performed by hardware components, such as thoseshown in FIGS. 1 and/or 2, or may be embodied in machine-executablecontent (e.g., instructions) 702, which may be used to cause ageneral-purpose or special-purpose processor or logic circuitsprogrammed with the instructions to perform the operations.Alternatively, the operations may be performed by a combination ofhardware and software. Moreover, although the invention has beendescribed in the context of a computing appliance, those skilled in theart will appreciate that such functionality may well be embodied in anyof number of alternate embodiments such as, for example, integratedwithin a communication appliance (e.g., a cellular telephone).

Many of the methods are described in their most basic form butoperations can be added to or deleted from any of the methods andinformation can be added or subtracted from any of the describedmessages without departing from the basic scope of the presentinvention. Any number of variations of the inventive concept areanticipated within the scope and spirit of the present invention. Inthis regard, the particular illustrated example embodiments are notprovided to limit the invention but merely to illustrate it. Thus, thescope of the present invention is not to be determined by the specificexamples provided above but only by the plain language of the followingclaims.

What is claimed is:
 1. In a base station that uses a number of antennasfor multiple-input multiple output (MIMO) transmission of orthogonalfrequency division multiplexed (OFDM) symbols through a channel, amethod for transmitting comprising: for the number of antennas,distributing quadrature-amplitude modulated (QAM) symbols across a groupof OFDM tones of a block comprising the group of tones and a group ofOFDM symbols; applying an incremented cyclic delay to the QAM symbols ofthe block associated with each subsequent of the antennas for acyclic-delay diversity (CDD) transmission; and providing the blocks fortransmission by an associated one of the antennas, wherein the cyclicdelay is a cyclic tone shift between the antennas that is based on aspatial correlation of the channel, and wherein a greater cyclic toneshift is used for greater spatial correlations.
 2. In a base stationthat uses a number of antennas for multiple-input multiple output (MIMO)transmission of orthogonal frequency division multiplexed (OFDM) symbolsthrough a channel, a method for transmitting comprising: for the numberof antennas, distributing quadrature-amplitude modulated (QAM) symbolsacross a group of OFDM tones of a block comprising the group of tonesand a group of OFDM symbols; applying an incremented cyclic delay to theQAM symbols of the block associated with each subsequent of the antennasfor a cyclic-delay diversity (CDD) transmission; and providing theblocks for transmission by an associated one of the antennas, wherein anumber of blocks of the CCD transmission is varied based on a delayspread of the channel.
 3. In a base station that uses a number ofantennas for multiple-input multiple output (MIMO) transmission oforthogonal frequency division multiplexed (OFDM) symbols through achannel, a method for transmitting comprising: for the number ofantennas, distributing quadrature-amplitude modulated (QAM) symbolsacross a group of OFDM tones of a block comprising the group of tonesand a group of OFDM symbols; applying an incremented cyclic delay to theQAM symbols of the block associated with each subsequent of the antennasfor a cyclic-delay diversity (CDD) transmission; providing the blocksfor transmission by an associated one of the antennas; and performingspace-frequency interleaving (SFI) on the blocks with an interleaverwherein a depth of the interleaver is based on a worst case channelresponse condition.
 4. A base station transmitter that uses a number ofantennas for multiple-input multiple output (MIMO) transmission oforthogonal frequency division multiplexed (OFDM) symbols through achannel, the base station transmitter comprising: for each of the numberof antennas, circuitry to distribute quadrature-amplitude modulated(QAM) symbols across a group of OFDM tones of the block comprising thegroup of tones and a group of OFDM symbols; circuitry to apply anincremented cyclic delay to the QAM symbols of a block associated witheach subsequent of the antennas for a cyclic-delay diversity (CDD)transmission; and circuitry to provide the blocks for transmission by anassociated one of the antennas, wherein the cyclic delay is a cyclictone shift between the antennas that is based on a spatial correlationof the channel, and wherein a greater cyclic tone shift is used forgreater spatial correlations.
 5. A base station transmitter that uses anumber of antennas for multiple-input multiple output (MIMO)transmission of orthogonal frequency division multiplexed (OFDM) symbolsthrough a channel, the base station transmitter comprising: for each ofthe number of antennas, circuitry to distribute quadrature-amplitudemodulated (QAM) symbols across a group of OFDM tones of the blockcomprising the group of tones and a group of OFDM symbols; circuitry toapply an incremented cyclic delay to the QAM symbols of a blockassociated with each subsequent of the antennas for a cyclic-delaydiversity (CDD) transmission; and circuitry to provide the blocks fortransmission by an associated one of the antennas, wherein a number ofblocks of the CCD transmission is varied based on a delay spread of thechannel.
 6. A base station transmitter that uses a number of antennasfor multiple-input multiple output (MIMO) transmission of orthogonalfrequency division multiplexed (OFDM) symbols through a channel, thebase station transmitter comprising: for each of the number of antennas,circuitry to distribute quadrature-amplitude modulated (QAM) symbolsacross a group of OFDM tones of the block comprising the group of tonesand a group of OFDM symbols; circuitry to apply an incremented cyclicdelay to the QAM symbols of a block associated with each subsequent ofthe antennas for a cyclic-delay diversity (CDD) transmission; circuitryto provide the blocks for transmission by an associated one of theantennas; and an interleaver to perform space-frequency interleaving(SFI) on the blocks, wherein a depth of the interleaver is based on aworst case channel response condition.
 7. A multiple-input multipleoutput (MIMO) transmitter for cyclic-delay diversity (CDD) transmissionof orthogonal frequency division multiplexed (OFDM) symbols through achannel comprising a diversity agent, wherein: for each of a number ofantennas, the diversity agent includes circuitry to distributequadrature-amplitude modulated (QAM) symbols across a group of OFDMtones of the block comprising the group of tones and a group of OFDMsymbols, wherein the diversity agent includes circuitry to apply anincremented cyclic delay to the QAM symbols of a block associated witheach subsequent of the antennas for a CDD transmission, wherein thediversity agent includes circuitry to provide the blocks fortransmission by an associated one of the antennas, wherein the cyclicdelay is a cyclic tone shift between the antennas that is based on aspatial correlation of the channel, and wherein a greater cyclic toneshift is used for greater spatial correlations.
 8. A multiple-inputmultiple output (MIMO) transmitter for cyclic-delay diversity (CDD)transmission of orthogonal frequency division multiplexed (OFDM) symbolsthrough a channel comprising a diversity agent, wherein: for each of anumber of antennas, the diversity agent includes circuitry to distributequadrature-amplitude modulated (QAM) symbols across a group of OFDMtones of the block comprising the group of tones and a group of OFDMsymbols, wherein the diversity agent includes circuitry to apply anincremented cyclic delay to the QAM symbols of a block associated witheach subsequent of the antennas for a CDD transmission, wherein thediversity agent includes circuitry to provide the blocks fortransmission by an associated one of the antennas, wherein a number ofblocks of the CCD transmission is varied based on a delay spread of thechannel, wherein the MIMO transmitter is part of a mobile station, andwherein the blocks are transmitted to a MIMO base station.
 9. Amultiple-input multiple output (MIMO) transmitter for cyclic-delaydiversity (CDD) transmission of orthogonal frequency divisionmultiplexed (OFDM) symbols through a channel comprising a diversityagent, wherein: for each of a number of antennas, the diversity agentincludes circuitry to distribute quadrature-amplitude modulated (QAM)symbols across a group of OFDM tones of the block comprising the groupof tones and a group of OFDM symbols, wherein the diversity agentincludes circuitry to apply an incremented cyclic delay to the QAMsymbols of a block associated with each subsequent of the antennas for aCDD transmission, wherein the diversity agent includes circuitry toprovide the blocks for transmission by an associated one of theantennas, and wherein the MIMO transmitter further comprises aninterleaver to perform space-frequency interleaving (SFI) on the blocks,wherein a depth of the interleaver is based on a worst case channelresponse condition.
 10. A base station transmitter that uses a number ofantennas for multiple-input multiple output (MIMO) transmission oforthogonal frequency division multiplexed (OFDM) symbols, the basestation transmitter comprising: for each of the number of antennas,circuitry to distribute quadrature-amplitude modulated (QAM) symbolsacross a group of OFDM tones of the block comprising the group of tonesand a group of OFDM symbols; circuitry to apply an incremented cyclicdelay to the QAM symbols of a block associated with each subsequent ofthe antennas for cyclic-delay diversity (CDD) transmission; circuitry toprovide the blocks for transmission by an associated one of theantennas; and an interleaver to perform space-frequency interleaving(SFI) on the blocks, wherein a depth of the interleaver is proportionalto a length of a channel impulse in time.
 11. A multiple-input multipleoutput (MIMO) transmitter for cyclic-delay diversity (CDD) transmissionof orthogonal frequency division multiplexed (OFDM) symbols comprising adiversity agent, wherein: for each of a number of antennas, thediversity agent includes circuitry to distribute quadrature-amplitudemodulated (QAM) symbols across a group of OFDM tones of the blockcomprising the group of tones and a group of OFDM symbols, wherein thediversity agent includes circuitry to apply an incremented cyclic delayto the QAM symbols of a block associated with each subsequent of theantennas for CDD transmission; and wherein the diversity agent includescircuitry to provide the blocks for transmission by an associated one ofthe antennas, and wherein the MIMO transmitter further includes aninterleaver to perform space-frequency interleaving (SFI) on the blocks,wherein a depth of the interleaver is proportional to a length of achannel impulse in time.